BTC Volatility History (x402, $0.05)

Full Bitcoin volatility time series (BTCUSDT 1d): realized volatility 30d + 90d (√365-annualized, calendar days) and ATR% (EMA-14). Each carries TWO percentile ranks and they answer different questions: the expanding rank (rvRank / atrPctAnnRank) runs from the start of history and is look-ahead-free, but BTC volatility has fallen structurally, so filtering on a low expanding rank mostly detects that decline rather than a regime; the rolling rank (rvRankRolling / atrPctAnnRankRolling, trailing 2 years) is the one for cross-epoch comparisons. History reaches back to 2011 via a stitched pre-Binance close series — ATR is null before meta.coverage.intraday_from because no daily high/low exists that far back, and it is left null rather than derived from closes (a synthetic ATR would understate the most volatile years of BTC history). meta.coverage reports series_start, intraday_from, rv_rows, atr_rows and sources. Compute-on-read from candles — descriptive, no signal. Same data as GET /api/v1/charts/volatility/history (paid call returns full history, no tier clamp).

Pricing: $0.05 USDC pay-per-call (x402). No account / no API key. Full compute-on-read time series (no persistence), recomputed from candles on read.